Method and apparatus for controlling a variable valve system

ABSTRACT

A variable valve timing apparatus for an internal combustion engine, includes an actuator ( 15 ) that operates a first variable valve timing mechanism; a detecting portion ( 35 ) that detects a driving position of the actuator ( 15 ); and a control portion ( 21 ) that executes an initialization process only when a preset execution condition is satisfied. In the initialization process, the control portion drives the actuator ( 15 ) to one end of a driving range and sets the driving position detected in this state as an initial value, and then drives the actuator ( 15 ) to an opposite end of the driving range and reflects an offset amount of the driving position detected in that state with respect to an optimum value in the driving position to compensate for the offset amount. The execution condition includes a condition that an increase amount in acceleration required of the internal combustion engine ( 1 ) be equal to or greater than a preset first determining value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a variable valve timing apparatus for aninternal combustion engine, and a control method of that variable valvetiming apparatus.

2. Description of the Related Art

One known variable valve timing apparatus for an internal combustionengine includes a variable valve timing mechanism that changes a valvecharacteristic of an engine valve such as an intake valve or an exhaustvalve, an actuator that is driven within a predetermined driving rangeto operate the mechanism, and an electronic control unit that drivinglycontrols the actuator.

In such a variable valve timing apparatus, in order to precisely controlthe valve characteristic of the engine valve, it is extremely importantto accurately detect the actual valve characteristic and operate thevariable valve timing mechanism, i.e., drivingly control the actuator,such that the actual valve characteristic comes to match a targetcharacteristic. The valve characteristic of an engine valve correspondsto the driving position of an actuator within the driving range, so oneway to detect the actual valve characteristic of an engine valve is toprovide a position sensor that detects the driving position of theactuator, and detect the actual valve characteristic of the engine valveusing the driving position of the actuator detected by the positionsensor. Incidentally, the driving position of the actuator detected bythe position sensor (i.e., or more accurately, information related tothe driving position) is stored in RAM of the electronic control unit.Then the information related to the driving position of the actuatorthat is stored in the RAM of the electronic control unit in this way isread from the RAM when necessary, such as when it is to be used todetect the actual valve characteristic of the engine valve.

However, the information related to the driving position of the actuatorto be used to detect the valve characteristic of the engine valve doesnot necessarily always correspond to the actual driving position of theactuator. That is, there are times when it may be off from the actualdriving position. For example, the information related to the drivingposition that is stored in the RAM of the electronic control unit may belost and reset to the initial value as a result of a temporaryinterruption (a so-called an instantaneous interruption) in the supplyof power to the electronic control unit temporarily or the like, or thecontent of the information may change. In this case, the informationrelated to the driving position of the actuator that is detected by theposition sensor, i.e., the driving position of the actuator that isstored in the RAM of the electronic control unit, will be inaccurate, sothe valve characteristic of the engine valve that is detected based onthis driving position information will also be inaccurate. As a result,if an attempt is made to control the valve characteristic of the enginevalve to the target characteristic by driving the actuator based on thedetected valve characteristic, this control will not be able to beperformed correctly.

In order to solve this problem, an initialization process to match thedriving position of the actuator detected by the position sensor withthe actual driving position of the actuator is executed when a presetexecution condition is satisfied. More specifically, this initializationprocess is executed according to steps 1 to 3 described below.

[Step 1]

The actuator is driven to one end of the driving range, and informationrelated to the driving position of the actuator stored in the RAM of theelectronic control unit i.e., the driving position detected by theposition sensor in this state, is set as an initial value.

[Step 2]

The actuator is driven to the end opposite the one end of the drivingrange, and the amount that the driving position of the actuator detectedby the position sensor in this state is offset from an optimum value isobtained.

[Step 3]

The amount that the detected driving position of the actuator is offsetfrom the optimum value is reflected in the driving position tocompensate for the offset amount. The resultant value after the offsetamount is reflected in the driving position is then stored as theinformation related to the driving position in the RAM of the electroniccontrol unit.

Incidentally, Japanese Patent Application Publication No. 2009-216052(JP-A-2009-216052) describes driving an actuator from one end of adriving range of the actuator to the opposite end of the driving rangewhen performing a process to match the driving position of an actuatordetected by a position sensor with an actual driving position.

Executing the initialization process described above does make itpossible to match the driving position of the actuator detected by theposition sensor with the actual driving position of the actuator.However, when the actuator is driven from one end of the driving rangeto the opposite end of the driving range in step 2 of thisinitialization process, the valve characteristic of the engine valve isinevitably greatly changed by the operation of the variable valve timingmechanism that occurs with this driving of the actuator. Also, thischange in the valve characteristic of the engine valve will greatlyaffect engine operation.

SUMMARY OF THE INVENTION

This invention thus provides a variable valve timing apparatus for aninternal combustion engine, and a control method of this variable valvetiming apparatus, that is capable of diminishing the effect that a largechange in a valve characteristic of an engine valve, that occurs when aninitialization process is executed, has on engine operation when thatlarge change occurs.

A first aspect of the invention relates to a variable valve timingapparatus for an internal combustion engine, that includes an actuatorthat operates a first variable valve timing mechanism that changes avalve characteristic of an engine valve; a detecting portion thatdetects a driving position of the actuator; and a control portion thatdrivingly controls the actuator within a driving range of the actuatorbased on the detected driving position, and executes an initializationprocess that matches the driving position of the actuator detected bythe detecting portion with an actual driving position of the actuatoronly when a preset execution condition is satisfied. In theinitialization process, the control portion drives the actuator to oneend of the driving range and sets the driving position detected by thedetecting portion in this state as an initial value, and then drives theactuator to an opposite end of the driving range that is opposite theone end of the driving range and reflects an offset amount, that is anamount that the driving position detected by the detecting portion whenthe actuator is driven to the opposite end is offset from an optimumvalue, in the driving position to compensate for the offset amount. Theexecution condition includes a condition that an amount of increase inacceleration required of the internal combustion engine be equal to orgreater than a preset first determining value.

In the structure described above, the first variable valve timingmechanism may include a variable valve lift mechanism that is operatedby the actuator and changes a maximum lift amount and an operation angleof an intake valve; and in the initialization process, the controlportion may drive the actuator to an end where the maximum lift amountand the operation angle of the intake valve are smallest, as the one endof the driving range, and then drive the actuator to an end where themaximum lift amount and the operation angle of the intake valve arelargest, as the opposite end of the driving range that is opposite theone end of the driving range.

In the structure described above, the variable valve timing mechanismmay change the maximum lift amount and the operation angle of the intakevalve in synchronization with each other by displacing a control shaftof the variable valve lift mechanism in an axial direction of thecontrol shaft.

In the structure described above, the actuator may include an electricmotor that displaces the control shaft in the axial direction.

The variable valve timing apparatus described above may also include asecond variable valve timing mechanism that changes a valvecharacteristic of an engine valve and that is operated by a drivingsource other than the actuator. In this case, the second variable valvetiming mechanism may include a variable intake valve timing mechanismthat changes a valve timing of the intake valve and a variable exhaustvalve timing mechanism that changes a valve timing of an exhaust valve.Further, the execution condition may also include a condition that anengine speed be equal to or greater than a preset second determiningvalue and an engine load be equal to or greater than a preset thirddetermining value, and a condition that an advance amount from a maximumretard angle of the valve timing of the intake valve be equal to or lessthan a preset fourth determining value, and a retard amount from amaximum advance angle of the valve timing of the exhaust valve be equalto or less than a preset fifth determining value.

In the structure described above, the control portion may adjust thevalve timing of the intake valve to the maximum retard angle and adjustthe valve timing of the exhaust valve to the maximum advance angle,before executing the initialization process.

In the structure described above, the execution condition may alsoinclude a condition that a change-allowing condition to allow the valvecharacteristic of the engine valve to be changed be satisfied.

In the structure described above, when the driving position detected bythe detecting portion is a position closer to the opposite end than asixth determining value when the execution condition is satisfied, thecontrol portion may execute the initialization process by setting acurrent driving position detected by the detecting portion as theinitial value of the driving position, and then driving the actuator tothe opposite end of the driving range and reflecting the offset amount,that is the amount that the driving position detected by the detectingportion when the actuator is driven to the opposite end is offset fromthe optimum value, in the driving position to compensate for the offsetamount.

In the structure described above, the sixth determining value maycorrespond to a center of the driving range.

A second aspect of the invention relates to a control method of avariable valve timing apparatus for an internal combustion engine. Thiscontrol method includes determining whether an amount of increase inacceleration required of an internal combustion engine is equal to orgreater than a preset first determining value; and executing aninitialization process that matches a driving position, that is detectedby a detecting portion, of an actuator that operates a variable valvetiming mechanism that changes a valve characteristic of an engine valve,only when the amount of increase in the acceleration required of theinternal combustion engine is equal to or greater than the firstdetermining value. The initialization process includes drivinglycontrolling the actuator to drive the actuator to one end of a drivingrange of the actuator; detecting the driving position at the one end ofthe driving range by the detecting portion when the actuator has beendriven to the one end of the driving range; setting the driving positionat the one end of the driving range detected by the detecting portion asan initial position; drivingly controlling the actuator to drive theactuator to an opposite end of the driving range that is opposite theone end of the driving range, after setting the initial value; detectingthe driving position at the opposite end of the driving range by thedetecting portion when the actuator has been driven to the opposite endof the driving range; identifying an offset amount that is an amountthat the driving position at the opposite end detected by the detectingportion is offset from an optimum value; and reflecting the offsetamount in the driving position at the opposite end detected by thedetecting portion to compensate for the offset amount.

According to the structures described above, when the valvecharacteristic of the engine valve greatly changes when theinitialization process is executed, the effect of that change on engineoperation can be diminished.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of theinvention will become apparent from the following description of exampleembodiments with reference to the accompanying drawings, wherein likenumerals are used to represent like elements and wherein:

FIG. 1 is an overall schematic diagram of an engine to which a variablevalve timing apparatus according to a first example embodiment of theinvention may be applied;

FIG. 2 is a timing chart showing a change in the lift amounts of anintake valve and an exhaust valve with respect to a change in the crankangle;

FIG. 3 is a timing chart showing a change in the lift amounts of theintake valve and the exhaust valve with respect to a change in the crankangle;

FIG. 4 is a timing chart showing a change in the lift amounts of theintake valve and the exhaust valve with respect to a change in the crankangle;

FIG. 5 is a flowchart illustrating an initialization process routineaccording to the first example embodiment; and

FIG. 6 is a flowchart illustrating an initialization process routineaccording to a second example embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS First Example Embodiment

Hereinafter, a first example embodiment in which the invention isapplied to a variable valve timing apparatus that varies a valvecharacteristic of an engine valve such as an intake valve or an exhaustvalve of a vehicle engine will be described with reference to FIGS. 1 to5.

In an engine 1 shown in FIG. 1, a throttle valve 13 is provided so as tobe able to open and close in an intake passage 3 that is connected to acombustion chamber 2. Air is drawn into a cylinder through this intakepassage 3 and fuel injected from a fuel injection valve 4 is suppliedinto the cylinder through the intake passage 3. When an air-fuel mixtureformed of this air and fuel is ignited by a spark plug 5, the air-fuelmixture combusts and the force generated from the combustion drives apiston 6 back and forth, such that a crankshaft 7 that serves as anoutput shaft of the engine 1 rotates. The combusted air-fuel mixture inthe cylinder is then discharged from the cylinder to an exhaust passage8 as exhaust gas.

In the engine 1, communication between the combustion chamber 2 and theintake passage 3 is opened or closed by an intake valve 9 that is oneengine valve of the engine 1 opening or closing. Similarly,communication between the combustion chamber 2 and the exhaust passage 8is opened or closed by an exhaust valve 10 that is another engine valveof the engine 1 opening or closing. The intake valve 9 opens and closeswith the rotation of an intake camshaft 11 that is rotated by thecrankshaft 7, and the exhaust valve 10 opens and closes with therotation of an exhaust camshaft 12 that is also rotated by thecrankshaft 7.

The engine 1 is provided with a variable intake valve timing mechanism16 provided on the intake camshaft 11, and a variable valve liftmechanism 14 provided between the intake camshaft 11 and the intakevalve 9. The variable intake valve timing mechanism 16 and the variablevalve lift mechanism 14 are variable valve timing mechanisms that varyvalve characteristics (i.e., the opening/closing characteristics) of theintake valve 9. The variable valve lift mechanism 14 changes a maximumlift amount and an operation angle of the intake valve 9 insynchronization with each other, as shown in FIG. 2, by displacing acontrol shaft 14 a of the variable valve lift mechanism 14 in the axialdirection: The control shaft 14 a is displaced in the axial direction byan actuator 15 that includes an electric motor and that converts therotary motion of the electric motor within a predetermined rotationangle range to linear motion in the axial direction of the control shaft14 a. The variable intake valve timing mechanism 16 (FIG. 1) is drivenby a driving source other than the actuator 15. More specifically, thevariable intake valve timing mechanism 16 is driven by controllinghydraulic pressure applied to the variable intake valve timing mechanism16 via a hydraulic circuit. The variable intake valve timing mechanism16 changes the relative rotation phase of the intake camshaft 11 (i.e.,the valve timing of the intake valve 9) with respect to the crankshaft 7by being driven. Driving the variable intake valve timing mechanism 16in this way advances or retards the valve opening timing and the valveclosing timing of the intake valve 9 while keeping the valve openingperiod (i.e., the operation angle) of the intake valve 9 constant, asshown in FIG. 3.

The engine 1 shown in FIG. 1 is also provided with a variable exhaustvalve timing mechanism 17 that is provided on the exhaust camshaft 12and that varies the relative rotation phase of the exhaust camshaft 12with respect to the crankshaft 7. This variable exhaust valve timingmechanism 17 serves as a variable valve timing mechanism that varies avalve characteristic (i.e., an opening/closing characteristic) of theexhaust valve 10. This variable exhaust valve timing mechanism 17 isalso driven by a driving source other than the actuator 15. Morespecifically, the variable exhaust valve timing mechanism 17 is drivenby controlling the hydraulic pressure acting on it via a hydrauliccircuit. Driving the variable exhaust valve timing mechanism 17 in thisway advances or retards the valve opening timing and the valve closingtiming of the exhaust valve 10 while keeping the valve opening period(i.e., the operation angle) of the exhaust valve 10 constant, as shownin FIG. 4.

Next, the electrical configuration of the variable valve timingapparatus of the engine 1 according to this example embodiment will bedescribed With reference to FIG. 1. This variable valve timing apparatusincludes an electronic control unit (ECU) 21 that executes variouscontrols related to the engine 1. The ECU 21 has a CPU that executesvarious calculations related to the controls, ROM in which data andprograms necessary for the controls are stored, RAM in which thecalculation results of the CPU and the like are temporarily stored, aninput port that receives signals from external devices, and an outputport that outputs signals to external devices, and the like.

Various sensors and the like are connected to the input port of the ECU21. Examples of some of these sensors are an accelerator position sensor28, a throttle position sensor 30, an airflow meter 32, a coolanttemperature sensor 33, a crank position sensor 34, a position sensor 35,an intake cam position sensor 36, and an exhaust cam position sensor 37.The accelerator position sensor 28 detects the operation amount (i.e.,the accelerator operation amount) of the accelerator pedal 27 that isdepressed by the driver of the vehicle.

The throttle position sensor 30 detects the opening amount (i.e., thethrottle opening amount) of the throttle valve 13 provided in the intakepassage 3. The airflow meter 32 detects the amount of air drawn into thecombustion chamber 2 the cylinder) through the intake passage 3.

The coolant temperature sensor 33 detects the coolant temperature of theengine 1. The crank position sensor 34 outputs a signal corresponding tothe rotation of the crankshaft 7. The information in this signal is usedto calculate the engine speed and the crank angle and the like.

The position sensor 35 detects the rotation angle that is a value withinthe predetermined rotation angle range of the electric motor of theactuator 15, as the driving position of the actuator 15. The intake camposition sensor 36 outputs a signal corresponding to the rotationalposition of the intake camshaft 11 based on the rotation of the intakecamshaft 11.

The exhaust cam position sensor 37 outputs a signal corresponding to therotational position of the exhaust camshaft 12 based on the rotation ofthe exhaust camshaft 12. Driving circuits and the like of the fuelinjection valve 4, the throttle valve 13, the variable valve liftmechanism 14 (i.e., the actuator 15), the variable intake valve timingmechanism 16, and the variable exhaust valve timing mechanism 17 and thelike are connected to the output port of the ECU 21.

Also, the ECU 21 ascertains the engine operating state based on thedetected signals input from the various sensors, and outputs commandsignals to the various driving circuits that are connected to the outputport according to the ascertained engine operating state. In this way,various operation controls of the engine 1, such as valve characteristicchanging control, throttle opening amount control, and fuel injectionquantity control of the engine 1 are executed via the ECU 21.

Incidentally, in order to precisely control the maximum lift amount andthe operation angle of the intake valve 9 as the valve characteristicsof the intake valve 9, it is extremely important to accurately determinethe current values of the maximum lift amount and the operation angle,and operate the variable valve lift mechanism 14, i.e., drivinglycontrol the actuator 15, such that the determined maximum lift amountand the determined operation angle come to match corresponding targetvalues. Here, the maximum lift amount and the operation angle of theintake valve 9 correspond to the driving position in the driving rangeof the actuator 15, or more specifically, the operation angle in apredetermined rotation angle range of the electric motor of the actuator15. Therefore, the current values of the maximum lift amount and theoperation angle of the intake valve 9 can be determined based on therotation angle of the electric motor of the actuator 15 detected by theposition sensor 35, i.e., the driving position of the actuator 15.Incidentally, the driving position of the actuator 15 detected by theposition sensor 35 (or more accurately, information related to thedriving position) is stored in RAM 21 a (FIG. 1) of the ECU 21. Thedriving position of the actuator 15 stored in the RAM 21 a of the ECU 21in this way is then read from the RAM 21 a when necessary, such as whenit is to be used to determine the current values of the maximum liftamount and the operation angle of the intake valve 9.

However, the information related to the driving position of the actuator15 that is detected by the position sensor 35 and stored in the RAM 21 adoes not necessarily always correspond to the actual driving position ofthe actuator 15. That is, it may be off from the actual drivingposition. For example, if the information related to the drivingposition stored in the RAM 21 a is lost and reset to the initial valueas a result of a temporary interruption (a so-called an instantaneousinterruption) in the supply of power to the ECU 21 or the like, or ifthe content of the information changes, the information related to thedriving position stored in the RAM 21 a will become off from the actualdriving position. If the information related to the driving positionstored in the RAM 21 a becomes inaccurate in this way, the actual valuesof the maximum lift amount and the operation angle of the intake valve 9that are determined based on the information of the driving positionwill also become inaccurate. In this case, if an attempt is made tocontrol the maximum lift amount and the operation angle of the intakevalve 9 to their target values by driving the actuator 15 based on thedetermined current values of the maximum lift amount and the operationangle of the intake valve 9, this control may not be able to beperformed correctly.

Therefore, an initialization process to match the driving position ofthe actuator 15 detected by the position sensor 35 to the actual drivingposition of the actuator 15 is executed. This initialization process isperformed according to steps 1 to 3 below.

[Step 1]

The actuator 15 is driven to one end of the driving range andinformation related to the driving position of the actuator 15 detectedby the position sensor 35 in this state, i.e., the driving positionstored in the RAM 21 a of the ECU 21, is set as an initial value.

[Step 2]

The actuator 15 is driven to the opposite end of the driving range thatis opposite the one end of the driving range, and an offset amount thatis the amount that the driving position of the actuator 15 detected bythe position sensor 35 in this state is offset from an optimum value isobtained.

[Step 3]

The offset amount that is the amount that the detected driving positionof the actuator 15 is offset from the optimum value is reflected in thedriving position to compensate for the offset amount. The resultantvalue after the offset amount is reflected in the driving position isthen stored as the information related to the driving position in theRAM 21 a of the ECU 21.

Executing this initialization process makes it possible to match thedriving position of the actuator 15 detected by the position sensor 35with the actual driving position of the actuator 15.

Next, the detailed steps for executing the initialization process,including the execution condition for the initialization process and thelike, will now be described with reference to the flowchart in FIG. 5that illustrates an initialization process routine. This initializationprocess routine is executed periodically by interruption atpredetermined intervals of time, for example, by the ECU 21.

In this routine, first it is determined whether a condition forexecuting the initialization process, i.e., an execution condition, issatisfied (step S101). Incidentally, this execution condition isdetermined to be satisfied when all of conditions 1 to 4, describednext, are satisfied.

[Condition 1]

Condition 1 is satisfied when an amount of increase in accelerationrequired of the engine 1 (hereinafter also simply referred to as “amountof increase in the required acceleration”) is equal to or greater than apreset determining value Ta. Incidentally, in this example embodiment,the amount of increase in the throttle opening amount is used as theamount of increase in the required acceleration. Also, the determiningvalue Ta may be set to the minimum value of the amount of increase inthe required acceleration at which a change in engine operation thatoccurs with the driving of the actuator 15 when the actuator 15 isdriven from the one end of the driving range to the opposite end of thedriving range according to step 2 can be regarded as relatively smallwith respect to a change in engine operation due to the increase in therequired acceleration. In this case, the determining value Ta is set,based on testing in advance or the like, to become such a value.

[Condition 2]

Condition 2 is satisfied when the engine speed is equal to or greaterthan a preset determining value Tb, and the engine load ratio is equalto or greater than a preset determining value Tc. This engine load ratiois a value that indicates the load ratio of the engine 1 that is basedon the total load state of the engine 1, and is a value within a rangeof 0 to 100%, inclusive, according to the load of the engine 1.Incidentally, the load of the engine 1 refers to the amount of air drawninto the combustion chamber 2 per one cycle of the engine 1, and isobtained based on detection signals from various sensors such as thethrottle position sensor 30, the accelerator position sensor 28, theairflow meter 32, and the crank position sensor 34. Incidentally, thedetermining values Tb and Tc may be set to the minimum values within arange where the combustion state of the engine 1 will not deterioratewhen the actuator 15 is driven according to step 2 of the initializationprocess. In this case, the determining values Tb and Tc are set, basedon testing in advance or the like, to become such values.

[Condition 3]

Condition 3 is satisfied when an advance amount from the maximum retardangle of the valve timing of the intake valve 9 is equal to or less thana preset determining value Td, and the retard amount from the maximumadvance angle of the valve timing of the exhaust valve 10 is equal to orless than a preset determining value Te. The advance amount from themaximum retard angle of the valve timing of the intake valve 9 isobtained based on signals output from the crank position sensor 34 andthe intake cam position sensor 36. Also, the retard amount from themaximum advance angle of the valve timing of the exhaust valve 10 isobtained based on signals output from the crank position sensor 34 andthe exhaust cam position sensor 37. Incidentally, the determining valuesTd and Te may be set to the maximum values within a range in which thecombustion state of the engine 1 will not deteriorate when the actuator15 is driven according to step 2 of the initialization process. In thiscase, the determining values Td and Te are set, based on testing inadvance or the like, to become such values.

[Condition 4]

Condition 4 is satisfied when a change-allowing condition to allow thevalve characteristics of the intake valve 9 and the exhaust valve 10 tobe changed is satisfied. When this change-allowing condition issatisfied, operation of the variable valve lift mechanism 14, thevariable intake valve timing mechanism 16, and the variable exhaustvalve timing mechanism 17 is allowed. On the other hand, when thischange-allowing condition is not satisfied, operation of the variablevalve lift mechanism 14, the variable intake valve timing mechanism 16,and the variable exhaust valve timing mechanism 17 is prohibited. It isdetermined that this change-allowing condition is satisfied when, forexample, the coolant temperature of the engine 1 is equal to or greaterthan a value indicating that the engine 1 has finished warming up.

Here, if even one of these four conditions, i.e., conditions 1 to 4, isnot satisfied, it is determined in step S101 that the executioncondition is not satisfied. If, on the other hand, it is determined instep S101 that the execution condition is satisfied based on all of thefour conditions, i.e., conditions 1 to 4, being satisfied, the valvetiming of the intake valve 9 is adjusted to the maximum retard angle andthe valve timing of the exhaust valve 10 is adjusted to the maximumadvance angle (step S102), after which the initialization processdescribed above is executed (step S103).

In step 2 of this initialization process, the actuator 15 is driven fromone end of the driving range to the opposite end of the driving range.More specifically, the actuator 15 is driven from the end where themaximum lift amount and the operation angle of the intake valve 9 arethe smallest (i.e., the Lo end) to the end where the maximum lift amountand the operation angle of the intake valve 9 are the greatest (i.e.,the Hi end). Therefore, in step 1 described above, the actuator 15 isdriven to the Lo end of the driving range, and information related tothe driving position of the actuator 15 detected by the position sensor35 in this state, i.e., the driving position stored in the RAM 21 a ofthe ECU 21, is set as an initial value. Also, in step 2 described above,the actuator 15 is driven to the Hi end, the amount that the drivingposition of the actuator 15 detected by the position sensor 35 in thisstate is offset from an optimum value (i.e., the offset amount) isobtained. Then in step 3 of the initialization process, this amount thatthe detected driving position of the actuator 15 is offset from theoptimum value is reflected in the driving position to compensate forthis offset amount. For example, the detected driving position of theactuator 15 is corrected based on this offset amount. The resultantvalue after the offset amount is reflected (corrected) in the drivingposition is then stored as the information related to the drivingposition in the RAM 21 a of the ECU 21.

With the detailed example embodiment described above, the followingeffects are able to be obtained.

(1) When the actuator 15 is driven from the one end (i.e., the Lo end)of the driving range to the opposite end (i.e., the Hi end) according tostep 2 during the initialization process, the maximum lift amount andthe operation angle of the intake valve 9 will inevitably greatly changeas a result of the operation of the variable valve lift mechanism 14that accompanies that driving of the actuator 15. Also, this change inthe maximum lift amount and the operation angle of the intake valve 9will greatly affect engine operation. However, because the executioncondition of the initialization process described includes Condition 1described “above,” the driving of the actuator 15 in the initializationprocess is performed under the condition that the amount of increase inthe acceleration required of the engine 1 is equal to or greater thanthe determining value Ta. When the amount of increase in theacceleration required of the engine 1 is large in this way, thefluctuation in the engine operation will also be large. Therefore, evenif the maximum lift amount and the operation angle of the intake valve 9greatly change due to the driving of the actuator 15 in theinitialization process, the effect from this change on the engineoperation will not stand out. In other words, when the fluctuation inthe engine operation becomes large as a result of an increase in theamount of increase in the acceleration required of the engine 1, theaffect on the engine operation from the driving of the actuator 15 inthe initialization process becomes relatively small. Accordingly, whenthe maximum lift amount and the operation angle of the intake valve 9greatly change due to the actuator 15 being driven from one end of thedriving range to the opposite end of the driving range during theinitialization process, the affect that this change has on the engineoperation can be kept small.

(2) In step 2 of the initialization process, the actuator 15 is drivenfrom the Lo end to the Hi end of the driving range of the actuator 15.This driving of the actuator 15 operates the variable valve liftmechanism 14 in the direction that increases the maximum lift amount andthe operation angle of the intake valve 9, i.e., in the direction thatincreases the amount of air drawn into (i.e., the intake air amount of)the engine 1. Therefore, the direction in which the engine operationchanges when the intake air amount of the engine 1 rapidly increases asa result of the amount of increase in the acceleration required of theengine 1 increasing to equal to or greater than the determining value Tais the same as the direction in which the engine operation changes whenthe intake air amount of the engine 1 increases due to the driving ofthe actuator 15 in the initialization process. Accordingly, the changein the engine operation when the amount of increase in the accelerationrequired of the engine 1 increases to equal to or greater than thedetermining value Ta makes it possible to keep the affect on the engineoperation from the driving of the actuator 15 in the initializationprocess even smaller.

(3) The intake air amount of the engine 1 is smaller when the enginespeed and the engine load ratio of the engine 1 are low. Also, when theadvance amount from the maximum retard angle of the valve timing of theintake valve 9 is large and the retard amount from the maximum advanceangle of the valve timing of the exhaust valve 10 is large, the valveoverlap of the intake valve 9 and the exhaust valve 10 is large. Also,when the intake air amount of the engine 1 is small and the valveoverlap is large, there tends to be a large amount of exhaust blowbackfrom the combustion chamber 2 of the engine 1 into the intake passage 3.If the actuator 15 is driven in the initialization process in thisengine operating state, the amount of exhaust blowback from thecombustion chamber 2 of the engine 1 into the intake passage 3 wouldincrease even more due to the increase in the valve overlap thataccompanies that driving of the actuator 15. As a result, the combustionstate of the engine 1 may deteriorate and adversely affect the operationof the engine 1 and the exhaust emissions.

In view of this, the execution condition of the initialization processincludes conditions 2 and 3 described above. Also, if at least one ofcondition 2 and condition 3 is not satisfied, the initialization processwill not be executed, so the actuator 15 will not be driven in theinitialization process.

A state in which condition 2 described above is not satisfied refers toa state in which at least one of i) the condition that the engine speedbe equal to or greater than the determining value Tb and ii) thecondition that the engine load ratio be equal to or greater than thedetermining value Tc is not satisfied, i.e., a state in which the intakeair amount of the engine 1 will decrease. Also, a state in whichcondition 3 described above is not satisfied refers to a state in whichat least one of i) the condition that the advance amount of the valvetiming of the intake valve 9 be equal to or less than the determiningvalue Td and ii) the condition that the retard amount of the valvetiming of the exhaust valve 10 be equal to or less than the determiningvalue Te is not satisfied, i.e., an engine operating state in which thevalve overlap of the intake valve 9 and the exhaust valve 10 willincrease.

In these states, the actuator 15 will not be driven in theinitialization process, so the exhaust blowback from the combustionchamber 2 of the engine 1 into the intake passage 3 that occurs withthat driving of the actuator 15 will not increase. As a result, thecombustion state of the engine 1 will not deteriorate, so there will beno adverse affect on the operation of the engine 1 and the exhaustemissions.

(4) When the execution condition is satisfied, the valve timing of theintake valve 9 is adjusted to the maximum retard angle and the valvetiming of the exhaust valve 10 is adjusted to the maximum advance angle,before executing the initialization process. As a result, the valveoverlap of the intake valve 9 and the exhaust valve 10 becomes theminimum value, so exhaust blowback from the combustion chamber 2 of theengine 1 into the intake passage 3 will not easily occur. Also, in sucha state, the actuator 15 is driven from the Lo end to the Hi end of thedriving range in the initialization process. Even though the valveoverlap tends to increase with this driving of the actuator 15, thevalve overlap will increase from the minimum value. Therefore, even ifthe valve overlap tends to increase with the driving of the actuator 15in the initialization process, exhaust blowback from the combustionchamber 2 of the engine 1 into the intake passage 3 resulting from thatincrease is inhibited from becoming excessively large. Thus,deterioration of the combustion state of the engine 1 caused by thisexhaust blowback is also suppressed.

(5) When there is a tendency for the valve overlap to increase with thedriving of the actuator 15 in the initialization process, the valveopening timing of the intake valve 9 is advanced, and as a result, thevalve 9 may contact the piston 6 of the engine 1. However, before theactuator 15 is driven, the valve timing of the intake valve 9 isadjusted to the maximum retard angle so that the valve opening timing ofthe intake valve 9 is retarded as much as possible. Therefore, even ifthe valve opening timing of the intake valve 9 is advanced due to thedriving of the actuator 15, contact between the intake valve 9 and thepiston 6 of the engine 1 at that time is inhibited.

(6) The execution condition of the initialization process includescondition 4 described above, i.e., that the change-allowing conditionthat allows the valve characteristics of the intake valve 9 and theexhaust valve 10 to be changed be satisfied. Therefore, theinitialization process is executed when the change-allowing condition issatisfied, i.e., when the valve characteristics of the intake valve 9and the exhaust valve 10 are actually able to be changed. Executing theinitialization process when the valve characteristics of the intakevalve 9 and the exhaust valve 10 are actually able to be changed in thisway enables the driving position of the actuator 15 detected by theposition sensor 35 to be more accurately matched with the actual drivingposition through the initialization process.

Second Example Embodiment

Next, a second example embodiment of the invention will be describedwith reference to FIG. 6. FIG. 6 is a flowchart illustrating aninitialization process routine of this example embodiment. In thisroutine, the processes (i.e., steps S201 and 5202) corresponding to 5101and 5102 of the initialization process routine (FIG. 5) in the firstexample embodiment are the same as they are in the first exampleembodiment, while the process (i.e., steps S203 to S205) correspondingto step S103 is different than it is in the first example embodiment.

In the initialization process routine shown in FIG. 6, it is firstdetermined whether a condition for executing the initialization process,i.e., an execution condition, is satisfied (step S201). If thedetermination here is yes, the valve timing of the intake valve 9 isadjusted to the maximum retard angle, and the valve timing of theexhaust valve 10 is adjusted to the maximum advance angle (step S202).

Then it is determined whether the current driving position of theactuator 15 detected by the position sensor 35 is a position closer tothe Lo end than the center of the driving range of the actuator 15(S203). If the determination here is yes, a first initialization processis executed as a process that is the same as the initialization processof the first example embodiment (step S204). If, on the other hand, thedetermination in step S203 is no, i.e., if it is determined that thecurrent driving position of the actuator 15 detected by the positionsensor 35 is a position closer to the Hi end than the center of thedriving range of the actuator 15, a second initialization process isexecuted (step S205).

This second initialization process differs from the initializationprocess of the first example embodiment (and thus the firstinitialization process) only with respect to step 1, from among steps 1to 3. More specifically, step 1a described next is executed instead ofstep 1 described above.

[Step 1a]

Information related to the current driving position of the actuator 15detected by the position sensor 35, i.e., the current driving positionstored in the RAM 21 a of the ECU 21, is set as it is as the initialvalue of the driving position.

Then, steps 2 and 3 described above are executed. As a result,information related to the driving position of the actuator 15 stored inthe RAM 21 a of the ECU 21 is matched with the actual driving position.

With this example embodiment, the effect described below, in addition toeffects (1) to (6) of the first example embodiment, are able to beobtained.

(7) An initialization process such as that described below (i.e., thesecond initialization process) is executed when the current drivingposition of the actuator 15 detected by the position sensor 35 is aposition closer to the Hi end than the determining value, e.g., when thecurrent driving position of the actuator 15 detected by the positionsensor 35 is a position closer to the Hi end than the center of thedriving range. That is, information related to the current drivingposition of the actuator 15 detected by the position sensor 35, i.e.,the driving position stored in the RAM 21 a of the ECU 21, is set as itis as the initial value of the driving position. Then, the actuator 15is driven to the Hi end, and the amount that the driving positiondetected by the position sensor 35 in this state is offset from anoptimum value is obtained. Then this offset amount is reflected in thedriving position detected by the position sensor 35 to compensate forthat offset amount. In this kind of second initialization process, theactuator 15 only needs to be driven a little, so the secondinitialization process can be completed quickly. Executing this kind ofsecond initialization process enables the driving position of theactuator 15 detected by the position sensor 35 to be matched with theactual driving position more quickly when this matching is performed.

Other Example Embodiments

Incidentally, the example embodiments described above may also bemodified as described below, for example. In the second exampleembodiment, the determination as to whether the current driving positionof the actuator 15 detected by the position sensor 35 is a position thatis closer to the Hi end is not limited to being a determination based onwhether the current driving position of the actuator 15 detected by theposition sensor 35 is a position that is closer to the Hi end than thecenter of the driving range of the actuator 15. For example, adetermining value may be set for a position that is closer to the Lo endthan the center of the driving range of the actuator 15, and it may bedetermined whether the current driving position of the actuator 15 iscloser to the Hi end than this determining value. In this case, if thecurrent driving position of the actuator 15 is closer to the Hi end thanthe determining value, it is determined that the current drivingposition is closer to the Hi end, so the second initialization processis executed.

In the first and second example embodiments, it is not absolutelyessential that steps S101 and S202 in the initialization processroutines be executed. Also, in the first and second example embodiments,the execution condition of the initialization process does notnecessarily have to include condition 2 described above.

In the first and second example embodiments, the execution condition ofthe initialization process does not necessarily have to includecondition 3 described above. Also, in the first and second exampleembodiments, the execution condition of the initialization process doesnot necessarily have to include condition 4 described above.

When driving the actuator 15 from one end of the driving range to theopposite end of the driving range in the initialization process of thefirst example embodiment and the first initialization process of thesecond example embodiment, that driving may also be from the Hi end ofthe driving range to the Lo end of the driving range.

In the first and second example embodiments, another parameter, such asthe amount of increase of an accelerator operation amount, may be usedinstead of using the amount of increase in the throttle opening, as theamount of increase in the acceleration required of the engine 1.

1. A variable valve timing apparatus for an internal combustion engine,comprising: an actuator that operates a first variable valve timingmechanism that changes a valve characteristic of an engine valve; adetecting portion that detects a driving position of the actuator; and acontrol portion that drivingly controls the actuator within a drivingrange of the actuator based on the detected driving position, andexecutes an initialization process that matches the driving position ofthe actuator detected by the detecting portion with an actual drivingposition of the actuator only when a preset execution condition issatisfied, wherein in the initialization process, the control portiondrives the actuator to one end of the driving range and sets the drivingposition detected by the detecting portion in this state as an initialvalue, and then drives the actuator to an opposite end of the drivingrange that is opposite the one end of the driving range and reflects anoffset amount, that is an amount that the driving position detected bythe detecting portion when the actuator is driven to the opposite end isoffset from an optimum value, in the driving position to compensate forthe offset amount; and the execution condition includes a condition thatan amount of increase in acceleration required of the internalcombustion engine be equal to or greater than a preset first determiningvalue.
 2. The variable valve timing apparatus according to claim 1,wherein the first variable valve timing mechanism includes a variablevalve lift mechanism that is operated by the actuator and changes amaximum lift amount and an operation angle of an intake valve; and inthe initialization process, the control portion drives the actuator toan end where the maximum lift amount and the operation angle of theintake valve are smallest, as the one end of the driving range, and thendrives the actuator to an end where the maximum lift amount and theoperation angle of the intake valve are largest, as the opposite end ofthe driving range that is opposite the one end of the driving range. 3.The variable valve timing apparatus according to claim 2, wherein thevariable valve lift mechanism changes the maximum lift amount and theoperation angle of the intake valve in synchronization with each otherby displacing a control shaft of the variable valve lift mechanism in anaxial direction of the control shaft.
 4. The variable valve timingapparatus according to claim 3, wherein the actuator includes anelectric motor that displaces the control shaft in the axial direction.5. The variable valve timing apparatus according to claim 2, furthercomprising a second variable valve timing mechanism that changes a valvecharacteristic of an engine valve and that is operated by a drivingsource other than the actuator, wherein the second variable valve timingmechanism includes a variable intake valve timing mechanism that changesa valve timing of the intake valve and a variable exhaust valve timingmechanism that changes a valve timing of an exhaust valve; and theexecution condition further includes a condition that an engine speed beequal to or greater than a preset second determining value and an engineload be equal to or greater than a preset third determining value, and acondition that an advance amount from a maximum retard angle of thevalve timing of the intake valve be equal to or less than a presetfourth determining value, and a retard amount from a maximum advanceangle of the valve timing of the exhaust valve be equal to or less thana preset fifth determining value.
 6. The variable valve timing apparatusaccording to claim 5, wherein the control portion adjusts the valvetiming of the intake valve to the maximum retard angle and adjusts thevalve timing of the exhaust valve to the maximum advance angle, beforeexecuting the initialization process.
 7. The variable valve timingapparatus according to claim 1, wherein the execution condition furtherincludes a condition that a change-allowing condition to allow the valvecharacteristic of the engine valve to be changed be satisfied.
 8. Thevariable valve timing apparatus according claim 1, wherein when thedriving position detected by the detecting portion is a position closerto the opposite end than a sixth determining value when the executioncondition is satisfied, the control portion executes the initializationprocess by setting a current driving position detected by the detectingportion as the initial value of the driving position, and then drivingthe actuator to the opposite end of the driving range and reflecting theoffset amount, that is the amount that the driving position detected bythe detecting portion when the actuator is driven to the opposite end isoffset from the optimum value, in the driving position to compensate forthe offset amount.
 9. The variable valve timing apparatus according toclaim 8, wherein the sixth determining value corresponds to a center ofthe driving range.
 10. A control method of a variable valve timingapparatus for an internal combustion engine, comprising: determiningwhether an amount of increase in acceleration required of an internalcombustion engine is equal to or greater than a preset first determiningvalue; and executing an initialization process that matches a drivingposition, detected by a detecting portion, of an actuator that operatesa variable valve timing mechanism that changes a valve characteristic ofan engine valve, with an actual driving position of the actuator onlywhen the amount of increase in the acceleration required of the internalcombustion engine is equal to or greater than the first determiningvalue, wherein the initialization process includes drivingly controllingthe actuator to drive the actuator to one end of a driving range of theactuator; detecting the driving position at the one end of the drivingrange by the detecting portion when the actuator has been driven to theone end of the driving range; setting the driving position at the oneend of the driving range detected by the detecting portion as an initialvalueposition; drivingly controlling the actuator to drive the actuatorto an opposite end of the driving range that is opposite the one end ofthe driving range, after setting the initial value; detecting thedriving position at the opposite end of the driving range by thedetecting portion when the actuator has been driven to the opposite endof the driving range; identifying an offset amount that is an amountthat the driving position at the opposite end detected by the detectingportion is offset from an optimum value; and reflecting the offsetamount in the driving position at the opposite end detected by thedetecting portion to compensate for the offset amount.